This invention relates generally to pneumatic lines and more particularly to pneumatic lines used in gas turbine engines.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. These gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work. An engine controller controls the amount of fuel that is supplied to the combustor. The engine controller monitors certain engine parameters to determine how much fuel should be provided. One of these parameters is the compressor discharge pressure (CDP), which provides an indication of how much compressed air is entering the combustor. The engine controller monitors the compressor discharge pressure by means of a pneumatic line referred to as the CDP line.
The CDP line directly carries compressed air from the compressor to the engine controller and thus provides a direct indication of the airflow of the compressor for use by the engine controller. Because the compressed air is derived from ambient air, it will contain varying amounts of water in vaporized form. Temperature and pressure changes often cause these water vapors to condense on the inside walls of the CDP line, and if large amounts of water condense, a substantial body of freestanding water can form inside the CDP line.
In a typical gas turbine engine, freestanding water could present difficulties in engine operation. Gas turbine engines are often exposed to subfreezing temperatures. The freestanding water could freeze in these conditions and block the CDP line, placing the engine at risk for a loss of thrust control event. To prevent such blockage, CDP lines have been provided with small, round drain holes at a low point in the line. When the CDP line carries pressurized air, the air blowing out of the drain hole effectively discharges excess water.
To prevent unacceptable losses of pressurized air, the drain holes are purposely made with a relatively small diameter. This, unfortunately, leads to problems when the engine is not in operation and the air in the CDP line is not pressurized. Compressed air will not blow out of the hole and, therefore, only the force of gravity will work to discharge water through the drain hole. However, surface tension of the water across the drain hole can actually support significant amounts of water inside the CDP line. It has been found that with no pressure differential across it, a 0.02 inch (0.0508 cm) diameter drain hole orifice will typically retain about 0.5 inches (1.27 cm) of water above it. This might be enough to plug the drain hole in the event that the water freezes.
To avoid this potential problem, U.S. Pat. No. 4,424,989, issued Jan. 10, 1984 to William R. Spencer et al., discloses a drain hole construction that prevents surface tension from supporting significant amounts of free-standing water in the drain hole. This drain hole construction comprises a divergent enlargement at the outer opening of the drain hole that prevents surface tension from inducing a build up of water inside the line.
However, CDP lines typically include internal features that can retain condensed water inside the CDP line and prevent it from draining to the drain holes. For instance, CDP lines are often designed with an in-line restrictor orifice that will limit gas discharge in the event that the line breaks upstream of the orifice. Because the restrictor orifice presents a greatly reduced diameter, water might not totally drain past the restrictor orifice. In cold conditions, this water could freeze and plug the orifice and the CDP line. Another feature that has been known to internally retain water is the manifold that connects the CDP line to the engine controller. The manifold presents sharp-edged reductions in diameters that can retain water. If this water were to freeze, it could also prevent the CDP signal from being delivered to the engine controller.
Accordingly, it would be desirable to have a pneumatic line in which water is allowed to freely drain within the line so as to be able to drain out of the line via the drain hole.
The above-mentioned need is met by the present invention, which provides an orifice formed inside the internal passage of a pneumatic line. To enhance drainage past the orifice, it comprises a first portion defining a diameter that is smaller than the diameter of the internal passage and a second portion that defines a progressively increasing diameter. Generally, a first end of the second portion has a diameter that is equal to the first portion diameter, and a second end of the second portion has a diameter that is equal to the internal passage diameter.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.